The present invention relates to an endodontic instrument adapted for use in performing root canal therapy on teeth.
Root canal therapy is a well-known procedure wherein the crown of a diseased tooth is opened so as to permit the canal to be cleaned and then filled. More particularly, as presently performed, a series of very delicate, flexible, finger-held instruments or files are used to clean out and shape the root canal, and each file is manually rotated and reciprocated in the canal by the dentist. Files of increasingly larger diameter are used in sequence, to achieve the desired cleaning and shaping. When the canal is thus prepared, it is solidly filled with a filling material, which typically comprises a waxy, rubbery compound known as gutta percha. In one procedure, the gutta percha is positioned on an instrument called a compactor, and the coated compactor is inserted into the prepared canal and rotated and reciprocated to compact the gutta percha therein. The dentist thereafter fills the tooth above the gutta percha with a protective cement, and lastly, a crown is fitted to the tooth.
Endodontic instruments of the described type were originally fabricated by permanently twisting a stainless steel rod of triangular or square cross section. The apices of the triangular or square cross section thus formed cutting edges which spiral along the length of the instrument. More recently, such instruments have been produced by a machining process, and wherein a cylindrical rod of stainless steel or nickel titanium alloy is cut into blanks of about two inches in length, and one end portion of each blank is tapered by machining the blank in a centerless grinding machine. Helical flutes are then machined on the tapered end portion, by moving the blank past a rotating grinding wheel and while the blank is slowly rotated to impart the desired helical configuration to the flutes. A cutting edge is thus formed along each side edge of each flute, and a helical land is preferably formed between the spiral flutes, as illustrated in U.S. Pat. No. 4,871,312 to Heath. A machining process as described above and which is particularly suitable for machining nickel titanium alloy is further described in U.S. Pat. Nos. 5,464,362 and 5,527,205 to Heath, et al., the disclosures of which are incorporated herein by reference.
Existing files of the described type typically comprise a shank which is composed of stainless steel or a nickel titanium alloy, and which has a length of about 30 mm (1.2 inches). The outer or proximate end of the shank mounts a conventional handle. The portion of the shank immediately below the handle is cylindrical and has a diameter of from about 0.5 and to about 1.6 mm (0.02 and 0.07 inches), and this shank portion includes calibrated depth markings of conventional design, note for example, U.S. Pat. No. 5,762,541 to Heath et al. The shank further includes an opposite distal or pilot end, and a working length is defined adjacent the pilot end. The working length may be cylindrical, or it may be slightly tapered toward the pilot end at an included angle of about one degree. The working length may have a length of about 2 mm (0.08 inches) up to the full length of the shank, i.e. about 30 mm (1.2 inches). In any event, the working length has a length sufficient to extend substantially the full depth of a tooth root canal, which typically is about 16 mm (0.63 inches).
In use, the dentist typically reaches into the mouth of the patient while gripping the handle of the instrument between two fingers. The pilot end of the shank is inserted in the root canal, and a repeating push-turn-pull motion is imparted to the instrument so that the cutting edges along the working length act to clean out and shape the root canal. During this procedure, the hand of the dentist visually obstructs the root canal, rendering it difficult to observe the calibration markings and thus the depth of penetration of the instrument into the canal.
It is accordingly an object of the present invention to provide an endodontic instrument which facilitates the viewing of the process within the mouth, by avoiding the need to insert the fingers of the dentist into the mouth of the patient.
It is a more particular object to provide an instrument of the described type which can be operated or manipulated by the dentist at a location outside of the mouth of the patient.